Risk perception studies have been ancillary to different fields of knowledge, trying to disclose the reasons behind the behaviors of people and predict their future actions [3]. Risk perception can be defined as a person’s judgement about a risk, influenced by facts, knowledge (lay and scientific), personal preferences and attitudes (dread, trust, and interpretation of uncertainty), individual assessments (general and specific), and his/her social role (defined as “agency” by sociological disciplines; that is, the possibility/ability to act to change one’s condition). Beliefs, knowledge, values, and attitudes not only influence decisions, but also behaviors, psychophysical conditions, and exposure attitudes of people to environmental pressures [3]. Risk perception is not entirely rational since people assess risks using a mixture of cognitive skills (weighing the evidence and using reasoning and logic to reach conclusions) and emotional appraisals (intuition or imagination) [4,5,6].

In the domain of the environment and health, the study of risk perception has acquired increasing relevance as part of the knowledge required to understand social contexts and specific personal dimensions of exposure to pollutants; risk perception is fundamental in environment and health risk communication because it determines which hazards people care about and how they deal with them [7,8,9,10]. It reinforces the importance of epidemiology in evaluating the health of communities living in areas where the main perceptible sources of pollution are known, even if the evidence produced always maintains some uncertainty [11].

Complexity and uncertainty are specific features of this research activity and the inclusion of people’s perspective in the process could help to enhance the global understanding and the use of research results [9,12,13,14,15,16,17].

Nothing in risk is neutral and its perception is linked to multiple facts and motivations. Social science research in risk perception has explored and discovered how risk is understood, manufactured, or created socially, politically, and culturally [7,8,9,18,19,20,21,22,23]. Additionally, the economic evaluation of savings through which it is possible to achieve remediating high-risk areas includes risk perception calculated through the Willingness to Pay (WTP) index as an indirect indicator of health expenses [24].

Ambient air pollution is the major environmental risk factor for the global disease burden, which has increased over the past 25 years, especially as a result of rising levels of pollution and increasing numbers of deaths from non-communicable diseases in low-income and middle-income countries [25].

Particulate matter (PM) comprises a class of pollutants consisting of a heterogeneous mixture of solid and liquid particles suspended in the air and it represents a considerable threat to health [26]. Primary PM can be released from both natural and anthropogenic sources, with road traffic considered the major source due to the erosion of pavements and abrasion of brakes and tires [27]. Secondary particles are products of the atmospheric transformation of nitrogen oxides and sulfur oxides, mainly emitted by traffic and the combustion of sulfur-containing fuels, respectively [28].

In 2013, the WHO International Agency for Research on Cancer (IARC) announced that there is sufficient evidence in humans for the carcinogenicity of outdoor air pollution and for PM in outdoor air pollution [29,30]. This understanding represented a turning point in research that focused on the health effects of inhalable PM, i.e., particles with diameters smaller than 10 (PM₁₀) or 2.5 micrometers (PM_2.5), and it was discovered that the size of particles is directly linked to their potential for causing health problems [31]. Human exposure to PM, both short and long term, has been quantitatively associated with numerous health effects, such as increased hospital admissions, emergency room visits, respiratory and cardiovascular morbidity, and mortality from cardiovascular and respiratory diseases and lung cancer [27]. Integrated exposure–response functions for each cause of death can be developed to estimate the relative risk of mortality attributable to PM. In particular, long-term exposure to PM_2.5 was estimated to have caused 4.2 million deaths in 2015, corresponding to 7.6% of the total global mortality and making PM_2.5 the fifth-ranking mortality risk factor [25].

For PM₁₀ and PM_2.5, concentration-response risk functions have been developed and proposed for health impact assessments. Many studies have included recommendations for actions and explorations of policy implications and the economic impact of PM reductions. Green energy policy in Europe includes air pollutant emission reduction in the motivation for reduction. Moreover, the international agreements addressing climate change consider PM in their reduction plans [32].

In several Asian cities, outdoor PM air pollution is increasing. In India, outdoor air pollution was responsible for more than 670,000 deaths in 2016. To deal with these health effects, several countries have launched large-scale policies, such as China [33,34] and India; in other countries like Thailand, there is a growing demand for policies to address the issue of polluted air [35]. Although in many countries there are no specific laws or protection rules, WHO guidelines are taken into consideration [28].

In China, to address the severe air pollution, the 2013 Action Plan on Prevention and Control of Air Pollution established a reduction of the PM_2.5 concentration in Beijing, Nanjing, and Guangzhou cities by 25%, 20%, and 15%, respectively, between 2012 and 2017. After this, several plans and specific measures were implemented [36].

In the EU and US, air protection policies are similar and the reduction of air pollution is a central element. In the US, air quality (AQ) is a federal matter and the relevant policies apply to the whole country. In the EU, AQ policy is based on standards issued by the European Commission and national implementations, where Member States determine the best way to achieve them within each country. In addition, in the US, air pollution management is implemented through a combination of the AQ standard and the emission standard strategies, whereas in the EU, emission standards, emission taxation, and cost-benefit analysis are used [37].

In 2013, the European Commission adopted a Clean Air Policy Package for Europe in order to set new objectives for EU air policy and reduce the negative health impacts of air pollution, such as respiratory diseases and premature death, by almost 50% by 2030 [38].

4. Big Data Utilization and Applications

5. Communication and Recommendations